The knowledge base for nursing intervention directed toward prevention of heart disease includes the ability to identify high risk groups on the basis of their risk factor profile and genetic predisposition. Toward this end, a longitudinal investigation of physiological (systolic and diastolic blood pressure, heart rate, serum lipids and lipoproteins relative weight), behavioral (Type A behavior and its components) and lifestyle (diet, activity, smoking) risk factors in twin children and their parents is proposed. A total of 120 families in two panels will be followed in this four year observational study, The first panel will be a subset of the six to eleven year old twins and their parents who were measured as part of a prior, cross-sectional study by the same investigators. They will be remeasured in 1988 and 1990. initial measurements on a second panel will be made in 1989 and remeasured in 1991. The interrelationships among risk factors, the extent to which they are due to environmental as opposed to genetic factors and their stability over time will be " investigated while accounting for changes in lifestyle variables, Specific aims include 1) modeling developmental changes in risk factor profiles as children move through adolescence, 2) partitioning the genetic and environmental sources of co-variation among risk factor, and 3) parent-child similarity on the Type A behavior pattern and specific components of it. Building on what is known about the profound changes that accompany puberty, there is a need to test whether there are concomitant changes in behavioral factor while accounting for parental risk factor levels and the potential impact of lifestyle factors. These results will guide public health nursing practice in the identification of high risk children and will contribute to the knowledge base for clinical nursing practice decisions directed toward disease prevention.